Fluid operated pump with hydraulic shock absorber



C. J. COBERLY FLUID OPERATED PUMP WITH HYDRAULIC SHOCK ABSORBER Dec. 4, 1951 3 Sheets-Sheet} Filed May 11, 1948 l/vve/vro/a Cm RENCE COBERLY BY HIS ATTORNEYS.

Dec. 4, 195] FLUID OPERATED PUMP WITH HYDRAULIC SHOCK ABSORBER Filed May 11,

C. J. COBERLY 3 Sheets-Sheet 2 CLHRENCf. d. C osz/eu BY HIS ATTORNY5.

Dec. 4, 1951 c. J. coBEhLY 2,576,924

FLUID OPERATED PUMP WITH HYDRAULIC SHOCK ABSORBER Filed May 11, 1948 3 Sheets-Sheet 5 PRESSURE TIME //v MENTOR.

CLARENCE d. Cosa/av BY HIS ATTORNEYS.

HARRIS, KlechgFos TR8HARRI6 Patented Dec. 4, 1951 FLUID OPERATED PUMP WITH HYDRAULIC SHOCK ABSORBER Clarence J. Coberly, Los Angeles, Calif., asslgnor, by mesne assignments, to Dresser Equipment Company, Cleveland, Ohio, a corporation of Ohio Application May 11, 1948, Serial No. 26,305

30 Claims.

My invention relates in general to apparatus for pumping fluids from wells and, more particularly, to an apparatus which includes -a reciprocating pump of the fluid operated type, a primary object of the invention being to provide an apparatus of this character having means associated therewith for absorbing fluid pressure variations which may impose hydraulic shock loads on the system.

Fluid operated pumps are used extensively in the oil industry for pumping oil from wells and are well known in the art so that a detailed description thereof herein is unnecessary, an example of such a pump being disclosed in my Patent No. 2,134,174, issued October 25, 1938. Briefly, such a fluid operated pump comprises a motor section and a pump section and is set in the well at the level from which oil is to be pumped. A power tubing for conveying operating fluid under pressure to the pump and a production tubing for conveying oil and other fluids discharged by the pump to the surface are connected to the motor and pump sections, respectively. The operating fluid is usually clean crude oil and will be referred to hereinafter as the power oil. For convenience, the combination of fluids pumped, which may include oil, water, etc., will be referred to hereinafter as the production fluid.

The motor section of the pump includes a cylinder having a piston therein and includes a suitable engine valve mechanism for admitting the power oil alternately to opposite ends of the motor cylinder so as to reciprocate the motor piston. The pump section includes a cylinder having a piston therein which is connected to the motor piston so that the reciprocatory motion of the motor piston is communicated to the pump piston. The latter draws fluid from the well and discharges it into the production tubing through suitable intake and exhaust valve mechanisms. Fluid operated pumps normally used in the oil industry are of the double acting type so that as well fluid is drawn into one end of the pump cylinder during a given stroke of the pump piston, well fluid drawn into the opposite end thereof during the preceding stroke is simultaneously discharged into the production tubing.

In order to prevent excessive wear and possible breakage of the various parts of a pump of this type, and in order to prevent possible damage to other components of the installation in which the pump is incorporated, it is essential to minimize any shock loads which may originate in the pump,

iii

the pump cylinder. The fluid entering the well casing from an adjacent oil producing formation may contain considerable quantities of natural gas, the amounts present depending upon the amounts present in the formation and depending upon prevailing conditions of pressure, temperature, etc. Sudden deccreases in the load on the pump piston may also result if the well is operated beyond its capacity so that air or gas is drawn into the pump cylinder as a result of the fluid level being drawn below the pump inlet. In some instances, the well casing may be connected to a vacuum line so that the pressure on the gas may be less than atmospheric. Also, in fields subjected to partial vacuums, air may be drawn into the well casing if it is left open.

Since the pump piston reduces the pressure in the pump cylinder below that prevailing in the well as it draws well fluid into the pump cylinder, any gas present in thewell fluid in solution or in suspension may be liberated in the pump cylinder with the result that a quantity of liquid sufficient only to partially fill the pump cylinder is drawn thereinto, the balance of the pump cylinder being filled with gas. Similarly, the pump cylinder may be partially filled with air or gas at a low pressure if the well is pumped beyond its capacity. Consequently, when the direction of movement of the pump piston is reversed, the pump piston acts only on the air or gas in the pump cylinder for at least a portion of the stroke. Since the air or gas is highly compressible, it offers but little resistance to movement of the pump piston so that the motor and pump pistons, being directly connected, may accelerate to an extremely high speed. In many instances, the speed attained by the pistons may greatly exceed their normal operating speed, the reason for this being that a considerable amount of potential energy is normally stored in the power oil supply system at the pressures usually employed because of the compressibility of the column of power oil in the power tubing and the expansibility of the power tubing. Such potential energy is released when the load on the pump piston decreases and may accelerate the motor and pump pistons to a speed far in excess of their normal operating speed.

When the pump piston, moving at an abnormally high speed, strikes liquid in the pump cyl-- inder, severe shock loads are developed which may cause extensive damage to the pump in the form of excessive wear, scoring, seizing and even breakage of parts. Moreover, pressure surges of considerable magnitude may be produced in the power oil and production fluid columns above the pump and may result in abnormal stressing of and possible damage to other components of the system. Also, if the well fluid being pumped contains a large percentage of water, which is frequently the case, shock loads originating in the pump may be particularly severe, the reason for this being that the compressibility of water is less than that of crude oil. Conseouentlv, when water is present, th compres ibility of the production fluid column above the pump is material- 1y reduced, as compared to the compre sibility of a production fluid col mn consisting of relatively pure crude oil. or a mixture of cru e oil and gas, so that the amount of en rgy which it is capable oi absorbing is materially decreased. Also, if air is drawn into the pump under shock loading conditions with water pres nt. both me hanical failure and corrosion are greatly accelerated for two reasons: first the presence of oxygen reduces the fati ue strength of the material; and. second, the hi h stresses produced by shock loads increase the chemical action at oints of maximum stress.

A governor located in close proximity to the pump may be employed to reduce the rate of flow of power oil to the motor section of the pump in re ponse to decreases in the load on the pump piston so as to reduce the piston speed whi h would otherwise be attained, an example of such a overnor bein disclosed in my Patent No. 2,311,157. i sued February 16, 1943. However, due to the fact that such a governor tends to op rate only after the condition which results in acceleration of the motor and pump pistons has already develo ed, there may be some lag in its operation. Consequently, even if a governor is employed, shock loads of undesirably large ma nitude may be produced, although such shock loads are, of course, greatly reduced as a result of the use of the gov rnor.

Even when a fiuid o erated pump of the type disclosed in my Patent No. 2,134.1'74, for example, is operating under normal conditions, i. e., when little or no gas or air is present in the well fluid being pumped, pressure pulsations are produced in both the power oil and the production fluid columns due to the fact that the motor and pump pistons stop momentarily at the ends of their stroke. This results in an increase in the pressure of the power oil and a decrease in the pressure of the production fluid. The amount of dwell at the ends of the stroke may be controlled with an,

engine valve of the type disclosed in my Patent No. 2,134,174, it being desirable to have suflicient dwell to allow time for the pump valves to seat. If the time allowed for the pump valves to seat is too great, excessive pressure pulsations in both the power oil and production fluid columns result, and, ii the time allowed is too small. serious pressure pulsations in the production fluid column result. It is impractical and, in many instances, impossible to eliminate such pressure pulsations by regulating the time allowed for th pump valves to seat. Althou h the magnitude of such pressure pulsations is small when the pump is operated at moderate speeds and when the pump cylinder fills properly, such pressure pulsations may be sumciently large to cause serious difiiculties at high pump speeds. Severe stresses may be developed in various components of the installation by the pulsations ii the frequency of the reciprocatory motion of the motor and pump pistons coincides with either the natural frequency of oscillation or one of the harmonics of either the power oil or the production fluid columns above the pump, i. e., if the frequency of the pressure pulsations developed in the columns as a result of the reciprocatory motion of the motor and pump pistons coincides with either the natural frequency or one oi the harmonics of one of the columns. These columns are only moderately damped so that standing pressure wave; of a magnitude sumcient to develop abnormal stresses in various components of the installation may be produced under such resonant operating conditions. 5 Since the natural frequencies of the power oil and production fluid columns are usually relatively low as compared to the frequency of reciprocation of the motor and pump pistons during normal operation, it is usually possible to avoid op erating the pump in phase with the natural frequencies of the columns. However, it is virtually impossible to select an operating speed for the pump which avoids both the natural frequencies of the power oil and production fluid columns and all of the harmonics thereof due to the fact that the intervals between the natural frequencies and the first harmonics and the intervals between harmonics are relatively small. Another factor which makes it difllcult to avoid both the natural frequency and all of the harmonics of the production fluid column in particular is that the nat= ural frequency of this column varies with varia= tions in the proportions of gas, oil and water in the production fluid. Consequently, since resonant operating conditions cannot be avoided readily by a selection of a suitable operating speed for the pump, it is desirable to reduce the magnitude of the pressure surges resulting from the reciprocatory nature of the operation of the pump so as to avoid producing standing pressure waves of excessive magnitude, the provision of an apparatus capable of absorbing such pressure surges being an important object of the present invention. I

In fluid operated pump installations of the type under consideration, the power oil and production fluid columns are semiclosed systems and do not communicate with each other freely in both directions because the fluid operated pump is interposed between them, the direction and amount of communication possible depending upon the positions of the engine and pump valves. With closed columns each terminating in a valve, serious water hammer may result from sudden closing of the valves with high fluid velocities. In

all cases of normal operation and some cases of shock resulting from malfunctioning of the pump valves or improper filling of the pump cylinder,

the pressure surges in the two columns are out Of 50 phase and may be cancelled out or greatly re= duccd by balancing the two columns against each other, which is another important object of my invention.

More specifically, an object is to provide a shoal: absorber which includes a movable fluid separating means, such as a piston, having opposed first and second surfaces which are exposed to the fluid pressures obtaining in the power tubing and the production tubing, respectively. With this construction, an increase in the pressure of the fluid in one of the tubings results in movement of the piston, or other fluid separating means, so that the fluid in the other tubing is compressed, whereby the energy producing such movement of the piston is absorbed.

Another object is to provide a shock absorber of the foregoing character wherein the piston is provided with a third surface which is exposed to a different fluid pressure, the fluid acting on 70 the third surface of the piston, which fluid is referred to hereinafter as the third or shock ab sorbing fluid, being confined so that it is compressed during movement of the piston in one direction and thus absorbs the energy producing 7 such movement of the piston.

My invention utilizes the principle that the amount of energy absorbed by a liquid as it is compressed is a function of the pressure of the liquid, an important object of the invention being to provide a shock absorber wherein the third or shock absorbing fluid is a liquid maintained at a very high pressure.

Another important object is to provide a shock absorber which includes pumping means for maintaining the pressure of the shock absorbing liquid at the desired value. A related object is to provide a pumping means which is carried by the shock absorber piston. Still another object in this connection is to provide such a pumping means which is fluid operated and which communicates with one end of the motor cylinder of the fluid operated pump so that as power oil is periodically admitted into said one end of the motor cylinder to operate the pump, it also operates the pumping means carreid by the shock absorber piston.

Other objects of the invention are to provide a shock absorber which may be connected directly to a pump with which it is to be used so that the piston therein may be exposed to the fluid pressures obtaining in the power tubing and the production tubing at points in close proximity to the pump, whereby pressure surges originating inthe pump are absorbed substantially instantaneously, and to provide a compact device which occupies a minimum of space in a well.

The foregoing objects of my invention and the advantages suggested thereby, together with various other objects and advantages which will become apparent, may be attained through the employment of the exemplary embodiment which is illustrated in the accompanying drawings and which is described in detail hereinafter. Referring to the drawings:

Fig. 1 is a vertical sectional view illustrating a pumping installation which embodies the invention as installed in a well;

Fig. 2 is an enlarged, vertical sectional vie taken along the broken line 22 of Fig. 1 and showing an upper portion of a shock absorber of the invention;

Fig. 3 is an enlarged, vertical sectional view taken along the broken line 3-3 of Fig. 1 and showing an intermediate portion of the shock absorber, Fig. 3 being a downward extension of Fig. 2;

Fig. 4 is an enlarged, vertical sectional view taken along the broken line 44 of Fig. 1 and showing another intermediate portion of the shock absorber, Fig. 4 being a downward extension of Fig. 3;

.Fig. 5 is an enlarged, vertical sectional view taken along the broken line 5-5 of Fig. 1 and showing the lower portion of the shock absorber connected to an upper portion of a fluid operated pump, Fig. 5 being a downward extension of Fig. 4;

Fig. 6 is a transverse sectional view taken alon the broken line 6-6 of Fig. 2;

Fig. '7 is a transverse sectional view taken along the broken line ii of Fig. 3;

Fig. 8 is a transverse sectional view taken along the broken line 8-8 of Fig. 5; and

Fig. 9 is a graph illustrating the operation of the shock absorber.

Referring particularly to Fig. 1 of the drawing, I show a well casing II] which extends downwardly from a casing head i i into an oil producing formation I2 of a well, the lower end of the casing being provided with perforations [3 through which well fluid, i. e., oil, water, gas, etc., from the oil producing formation may flow into the casing. A

production tubing I4 is suspended from a tubing head l5 which forms an intermediate part of the casinghead H and extends downwardly through the casing l0 into a body I6 of well fluid in the lower portion thereof. The lower end of the production tubing I4 is equipped with a pump seat I! which is adapted to receive and support the inlet end iii of a fluid operated pump l9. A power tubing 20 for conveying power oil to the pump i9 is suspended from a cap member 2i of the tubing head i5 and extends downwardly through the production tubing Hi. In the particular construction illustrated in the drawings, the power tubing 20 is connected to the pump is through a shock absorber or cushioning device of the invention which is indicated generally by the numeral 22 and is described in detail hereinafter.

The fluid operated pump i9 per se forms no part of the present invention and is not shown in complete detail in the drawings. The pump ill may, for example, be of the type disclosed in my aforesaid Patent No. 2,134,174, or may be of any other suitable type, as is well known in the art. As best shown in Fig. 1 of the drawings, the pump it includes, in general, an engine or motor piston 26 which is reciprocable in a motor cylinder 21, and includes a pump piston 28 which is reciprocable in a pump cylinder 29, the two pistons being directly connected by a rod 30. Connected to and extending upwardly from the motor piston 26 is a pilot rod 3i, and connected to and extending downwardly from the pump piston 28 is a lower rod 32. As best shown in Fig. 5 of the drawings, the pump 19 is provided with a valve chamber 35 therein which communicates with the interior of the shock absorber 22, the latter being adapted to convey power oil from the power tubing 20 to the valve chamber in a manner to be discussed in more detail hereinafter. The pump is is provided with a pair of passages, indicated generally by the numerals 31 and 38, which respectively connect the valve chamber 35 to the upper and lower ends of the motor cylinder 21, each of the passages 31 and 38 preferably comprising a plurality of individual passages only one of which is shown in the drawings. The pump i9 is also provided with a discharge passage 39 which leads from the valve chamber 35 to the exterior of thepump and communicates with the interior of the production tubing M, the passage 39 also preferably comprising a plurality of individual passages. ,Slidably disposed in the valve chamber 35 is an engine valve 40 of the piston type which is adapted to admit power oil alternately into opposite ends of the motor cylinder 21 through the passages 31 and 38, and which is adapted to connect opposite ends of the motor cylinder alternately to the discharge passage 39 leading to the production tubing 114. As will be apparent, when the piston valve 40, which is shown more or less diagrammatically, is in the position shown in Fig. 5 of the drawings, it admits power oil to the lower end of the motor cylinder 21 through the passage 38 and connects the upper end thereof to the discharge passage 39, the piston valve being adapted to move downwardly to a position (not shown) wherein it admits power oil into the upper end of the motor cylinder through the passage 31 and connects the lower end thereof to the discharge passage.

The foregoing discussion of the engine valve mechanism for controlling admission of the power oil to and discharge thereof from the motor cylinder 21 is intended merely as a general do scription of its structure and operation since. per se, it forms no part of the present inven tion. For a detailed description of the structure and operation oi! a suitable engine valve mechanism, reference is made to my aforesaid Patent No. 2,134,174.

The general operation of the pump is is well known in the art, being described in detail in my Patent No. 2,134,174, and needs be described only briefly herein. The powed oil, which is preferably clean crude oil, is delivered under pressure to the casing head Ii through a supply pipe 4| and flows downwardly through the power tubing 20 to the pump l9, the power oil flowing through the shock absorber 22 as will be discussed in more detail hereinafter. The power oil is admitted alternately into opposite ends or the motor cylinder 21 by the previously discussed engine valve mechanism so as to reciprocate the motor piston 2|, the reciprocatory motion of the motor piston being communicated to the pump piston 28 by the intermediate rod 30. Well fluid from the body I6 is introduced alternately into opposite ends of the pump cylinder 29 by a suitable pump valve mechanism (not shown) and is discharged into the production tubing It as production fluid by the pump piston 28, the production fluid subsequently flowing upwardly through the production tubing to the surface. The production fluid flows from the production tubing l4 into a discharge pipe 42 which may lead to a point of use or storage. 7

With the foregoing general description of the structure and operation of an installation in which my shock absorber 22 may be incorporated in mind, the shock absorber itself will now be considered. In general, the device includes a movable fluid separating means which is exemplified as a piston 43, shown in Fig. 3. and which is reciprocable vertically in a cylinder 44, the lower end of this cylinder being adapted to receive power oil at operating pressure therein, and the upper end of this cylinder being adapted to receive production fiuid therein. The shock absorber piston 63 is provided with a surface 4'17, shown in Fig. 2, which is adapted to be exposed to a fluid pressure greatly exceeding the pressures of the power oil and production fluid, the fluid acting on this surface of the piston being a liquid which is confined in a chamber d8 in the particu lar construction illustrated. The shock absorber 22 also includes fluid operated pumping means 49, shown in Fig. 3, carried by the piston 33 for maintaining the pressure and vole oi the liquid in the chamber its at the desired value, the pping means d9 being operated by the power oil periodically admitted into one end of the motor cylinder 21! as will be discussed in more detail hereinafter.

Considering the shock absorber 22 in more detail with particular reference to hide. 2 to of the drawings, it includes a housing which is formed in three sections (50, 52 and 53 for convenience in manufacture, the three sections of the housing being tubes arranged end-to-end in the particular construction illustrated. The up per-most tube it is threadedly connected at its upper end to a fitting as which, in turn, is threadedly connected to the lower end of the power tubing 2d, the fitting lid being provided with a passage 55 therethrough to admit power oil into the tube Eli. The tubes bi and 52 are threadedly connected by a fitting 56 and the tubes 52 and 58 are ariy connected by a die iii! ting 57. the tube 53 being threadedly connected at its lower end to a fitting 58 which, in turn, is threadedly connected to the upper end 01' the pump is. As best shown in Figs. 2, 3 and 8 of the drawings, the fitting 5B connecting the tubes BI and 52 is provided with a plurality of longitudinal passages 6| therethrough which conduct power oil from the tube 5| to the tube 52, and is provided with a depending tubular extension 82 which is spaced from the inner wall or the tube 52 to provide an annular passage 83 for the power oil. The fltting 51 connecting the tubes 52 and 53 is provided with an upwardly directed tubular extension 64 which is inserted into the lower end of the tubular extension 62 o! the fitting 58 and which is spaced from the inner wali of the tube 52 to provide an annular passage It for the power oil, the fittin 51 bein provided with a plurality of longitudinal passages lit through which the power oil may flow from the annular passage 85 into the tube 53. The fitting 58 connecting the tube 53 to the pump it receives an insert 10 having a frusto-conical seat 1! which engages a frusto-conical surface 12 at the upper end of the pump, the insert I0 being provided with an annular shoulder 13 which is adapted to seat against an annular shoulder H on the fitting 58 to prevent upward movement of the insert. Rotation of this insert is prevented by key-like projections 15 thereon which are disposed in complementary keyways 16 in the fitting 58. The insert i0 is provided with an opening therethrough which receives the pilot rod 3!, the diameter of this opening being greater than that of the pilot rod so as to provide an annular passage communicating at one end with the in terior of the tube 53 and at its other end with the valve chamber 35 in the pump 69. With the foregoing construction, it will be apparent that the power oil may flow from the power tubing 20 to the valve chamber 35 by way of the passage 5% through the fittin 54, the tube 55, the passages 6i through the fitting 56, the annular passages 83 and 65 around the tubular extensions 62 and 8d of the fittings 58 and 5?, the passages 66 through the fitting 51, the tube 63, and the annular passage ll through the insert 70. From the valve chamber 35, the power oil is admitted alternately into opposite ends of the motor cylinder 2? by the engine valve it in the manner previously discussed.

Referrin particularly to Figs. 2 and 3 or the drawings, the depending tubular extension 62 of the fitting 5% forms the previously mentioned cyiinder N for the shock absorber piston $3, the

cylinder as being closed at its lower end by the upper end of the tubular extension 63 of the fitting 5i, and being closed at its upper end by a tubular fitting :18 threaded into the upper end thereof. In the particular construction illustrated in the drawings, the chamber 48 for the liquid which acts on the surface d7] of the pmton 83 has a bottle-like configuration and is provided with a neck which is threaded into the upper end of the tubular fitting I8.

As best shown in Figs. 2 and 6 of the drawings. a plurality of radial passages an in the fitting 56 provide fluid communication between the production tubing M and the upper end of the cylinder 44 so that the pressure of the production fluid tends to move the piston 43 downwardly, and, as best shown in Fig. 3 of the drawings, a plurality of radial passages 82 in the tubular extension 62 of the fitting 56 provide fluid communication between the annular passages 63 for the power oil and the lower end of the cylinder 44 so that the pressure of the power oil tends to move the piston upwardly.

Referring particularly to Figs. 2 and 3 of the drawings, the surface 41 of the shock absorber piston 43, which surface is exposed to the pressure of the liquid in the chamber 48, is formed by the upper end of an upwardly extending, tubular stem 85 on the piston 43, the stem 85 extending through the tubular fitting 18 into the neck 88 of the bottle-like chamber 48 and being substantially sealed with respect to the fittinglB by packing 86. The piston 43 is provided at its upper and lower ends with conuterbores 81 and 88 which are connected by an intermediate bore 89, the counterbores 81 and 88 having threaded thereinto and being closed by tubular plugs 98 and 9|, respectively. The stem 85 on'the piston 43 extends through the tubular plug 98 and is provided with a head 92 thereon which is seated against the inner end of this plug. As will be discussed in more detail in the following paragraphs, the fluid operated pumping means 49 is disposed in the counterbore 81 and the bore 89 in the shock absorber piston 43 and is adapted to deliver a liquid, preferably oil obtained from the power oil supply, into the chamber 48, through the tubular stem 85 so as to maintain the pressure and volume of oil in the chamber 48 at the desired value. 4

Considering the pumping means 49 in more detail, the bore 89 in the piston 43 serves as a cylinder for an auxiliary piston 95, the cylinder 89 being closed at its upper end by an insert 95 which is seated against a shoulder 91 formed at the junction of the cylinder 89 and the counterbore 81, and being closed at its lower end by an insert 98 which is seated against a shoulder 99 formed at the junction of the counterbore 88 and the cylinder 89. The insert 98 is provided with a passage I88 therethrough which communicates with the interior of a downwardly extending tubular stem I8I on the piston 43, the stem I8I extending through the tubular plug 9| and being provided with a head I82 thereon which is seated against the outer end of the insert 98 and the inner end of the plug SL The tubular stem I8I communicates with one end of the motor cylinder 21 in the pump I9 in a manner about to be described so that the fluid pressure obtaining in such end of the motor cylinder also obtains in the lower end of the cylinder 89 containing the auxiliary piston 95, the stem I8I communicating with the upper end of the motor cylinder in the particular construction illustrated although it may communicate with either end thereof.

Referring particularly to Figs. 3 and 4 of the drawings, the tubular stem I8I extends downwardly into a sectional liner I84 in the tubular extension 64 of the fitting 51. The liner I84 is provided with a plurality of longitudinal grooves I85 in its exterior surface, these grooves communicating with the interior of the liner at their lower ends through ports I86, and communicating with the interior of the liner at their upper ends through ports I81. The liner I84 includes a section I88 having an internal diameter which is greater than the external diameter of the tubular stem I8I so as to provide an annular space I89 which communicates with the ports I81 at the upper ends of the grooves I85. The tubular stem IN is provided with a plurality of radial passages II8 therein which are adapted 'the bore H2.

to register with the annular space I89 to provide fluid communication between the interior of the tubular stem and the lower end of the liner I84 by way of the ports I86, the grooves I and the ports I81. It will be noted that as the shock absorber piston 43 moves downwardly, the radial passages I II] in the tubular stem IUI move out of registry with the annular space I89 to prevent such nuid communication, the reason for this being discussed hereinafter.

As best shown in Fig. 4 of the drawings, the fitting 51 is provided with a bore H2 at its lower end which communicates with the interior of the liner I84, a fitting II3 being threaded into Connected to the fitting H3 is the upper end of a conduit or tube II4 which is secured at its lower end to the insert 18 in the fitting 58 which connects the tube 53 of the shock absorber housing to the upper end of the pump I9. The tube H4 is provided with a coiled portion I I5 intermediate its ends for convenience in assembling the shock absorber 22, the coiled portion of the tube II4 tending to seat the shoulder 13 on the insert l8 against the complementary shoulder I4 on the fitting 58 during assembly, as will be discussed in more detail hereinafter. The tube I I4 communicates at its lower end with a passage IIB through the insert I8, the passage III;- communicating with a passage Ill in the pump I9 which, in turn, communicates with the passage 31 leading to the upper end of the motor cylinder 21 by way of the valve chamber 35 in the pump. It will be apparent that the fluid pressure obtaining in the upper endof the motor cylinder 21 is thus communicated to the lower end of the cylinder 89 in the shock absorber piston 43 and is thus applied to the lower end I83 of the auxiliary piston 95.

The auxiliary piston is provided with an upwardly directed stem I2I which extends through a bore I22 in the insert 96 into a counterbore I23 therein, the stem making a tight fit with the bore I22. This construction provides the auxiliary piston with an annular surface I24 at its upper end which is equal in area to the diiference in the cross-sectional areas of the piston and the stem I2I. As best shown in Figs. 3 and 7, the annular surface I24 is exposed to the pressure of the production fluid by means of a plurality of passages I25 in the shock absorber piston 43 which communicate at their lower ends with the upper end of the cylinder 89 for the auxiliary piston 95 and which communicate at their upper ends with the upper end of the cylinder 44 for the piston 43.

Referring particularly to Fig. 3 of the drawings, the pumping means 49 includes check valves I33 and I34 interposed between the insert 96 and the head 92 on the tubular stem 85, the check valve I33 being provided with a, passage I35 which terminates at one end in a seat I36 for a ball valve I31 and which communicates at its other end with an annular groove I38. The groove I38 registers with the upper ends of a plurality of passages I39 in the shock absorber piston 43, as best shown in Figs. 3 and '7 of the drawings. The passages I39 communicate at their lower ends with the lower end of the cylinder 44 so that power oil may flow from the lower end of the cylinder 44 to the check valve I33. The latter is provided with a passage I42 which terminates at one end in the seat I36 for the ball valve I31 and which communicates at its other end with a passage I43 in the check valve I34, the passage I43 terminating in a seat I44 for a ball valve I45.

From the seat I44, a passage I48 extends through the check valve I34 and communicates with the lower end of the tubular stem 85. The check valve I33 is provided with another passage I41 which communicates at one end with the passage I42 therein and which communicates at its other end with the counterbore I23 in the insert 96. It will be noted that the head 92 and the body of the check valve I33 are respectively provided with milled slots I48 and I49 therein at the upper ends of the passages I46 and I42, respectively, the widths of these slots being less than the diameters of the ball valves I45 and I31 to prevent seating of the ball valves at the upper ends of the passages mentioned.

The foregoing completes the description of the structure of the shock absorber 22 and the installation in which it is incorporated, and the operation of the shock absorber will now be considered, the operation of the pumping means 49 being considered first for convenience. It will be apparent that the upper end of the stem I2I on the auxiliary piston 95 is always exposed to a fluid pressure at least equal to the power oil pressure due to the fact that the ball valve I3! is arranged to be lifted ofi its seat I38 by the pressure of the power oil in the passage I35 in the check valve I33, the passage I35 communicating with the lower end of the shock absorber cylinder 44 through the annular groove I38 and the passages I 39 as previously discussed. The annular surface I24 at the upper end of the auxiliary piston 95 is always exposed to the production fluid pressure through the passages I25 connecting the upper end of the cylinder 89 to the upper end of the cylinder 4 3. Thus, the auxiliary piston 95 is always subjected to a downward force which is equal to the product of the area of the annular surface I24 and the production fluid pressure plus the product of the area of the upper end of the stem I2I and a fluid pressure at least equal to the power oil pressure.

As previously discussed, the lower end of the cylinder 89 for the auxiliary piston 95 communicates with the upper end of the motor cylinder 21 in the pump It so that the same fluid pressure obtains in the lower end of the cylinder 89 as obtains in the upper end of the motor cylinder, which fluid pressure varies between the power oil pressure and the production fluid pressure under the control of the engine valve 00. Thus, the auxiliary piston is subjected to an upward force which alternates between a value equal to the product of the cross-sectional area of the piston and the production fluid pressure and a value equal to the product of the cross-sectional area of the piston 69 and the power oil pressure. Consequently, when the lower end I03 of the auxiliary piston 95 is exposed to the power oil pressure, the auxiliary piston will move upward= ly in its cylinder and when it is exposed to the production fluid pressure, as shown in Fig. 5, the auxiliary piston will move downwardly in its cylinder. Since the pressure applied to the lower end I03 of the auxiliary piston alternates be= tween the power oil pressure and the production fluid pressure, a reciprocatory motion of the auxiliary piston results to pump oil from the power oil supply into the chamber l0.

Considering the manner in which the auxiliary piston 95 pumps oil into the chamber 98, it will be apparent that as the auxiliary piston moves downwardly, oil from the power oil supply flows into the counterbore 02th; the insert 98 past the ball valve I371, flow from the chamber 48 iv downwardly movement of the auxiliary piston being prevented by the ball valve I45. During upward movement of the auxiliary piston 95, the stem I2I forces at least a part of the oil in the counterbore I23 past the ball valve I45 and into the chamber 48 through the tubular stem 85, flow back into the passages leading to the lower end of the shock absorber cylinder 44 being prevented during upward movement of the auxiliary piston by the ball valve I31. Thus, it will be apparent that for each complete cycle of movement of the auxiliary piston 95, a quantity of oil from the power oil supply is introduced into the cham-= ber 48 to maintain the desired pressure and vol= ume therein, the quantity introduced being sui ficient to replace any oil escaping from the cham= her as by leakage past the packing encircling the tubular stem 85.

It will be understood that although the fluid operating pumping means 49 is shown as adapted to pump oil from the power oil supply into the chamber 48, it may be designed to pump production fluid thereinto, or to pump fluid from an independent source thereinto. However, I prefer to employ oil from the power oil supply as it is normally cleaner than the production oil.

For reasons which will be discussed in more detail hereinafter, the pressure in the chamber 48 is maintained at a high value, e. g., preferably at a value of the order of magnitude of from 25,000 to 50,000 pounds per square inch. As will be apparent to those skilled in the art, any de= sired value for the pressure in the chamber 60 may be attained by suitably relating the areas of the auxiliary piston and the stem I2I thereon to the power oil and production fluid pressures. For example, if the difference between the power oil and production fluid pressures is 1,250 pounds per square inch, a construction wherein the ratio of the area of the annular sur face I24 of the auxiliary piston 95 to the cross sectional area of the stem I2I thereon is 2021 will produce a pressure of approximately 25,000 pounds per square inch in the chamber 48. In other words, the pumping means 49 will have an amplification factor of twenty in this example.

' Considering the over-all operation of the shock absorber 222, it will be apparent that the pressure of the power oil in the lower end of the cylinder Ml tends to move the shocir absorber piston 63 upwardly while the pressure of the production fluid in the upper end of the cylinder 64 and the pressure of the oil in the chamber as tend to move the shock absorber piston downwardly. The piston 93 is balanced when normal operating conditions for the pump it) prevail, but, if the relative fluid pressures obtaining in the produc tion and power tubings [Hi and 2a vary, the piston 03 becomes unbalanced and moves either up-= wardly or downwardly in its cylinder MI, depend= ing upon the direction of unbalance. If, for e::-= ample, the unbalanced force acts upwardly, the energy producing the force is absorbed by connpression of the oil in the chamber 48 and also by compression of; the production fluid. Con= versely, if the unbalanced force acts downwardly, the energy producing same is absorbed by compression of the power oil. Thus, variations in the relative fluid premures obtaining in the pro= duction and power tubings I4 and 29 which might otherwise produce hydraulic shock loads having detrimental efiects are absorbed.

Such variations in the relative fluid pressure may arise from various sources. For example, it air or gas is present in the pump cylinder 29, the

motor piston 26 and the pump piston 28 may, as previously discussed, accelerate to an excessive speed so that a pressure surge in the production tubing I4 may result when the pump piston strikes solid well fluid. Also, pressure pulsations may be produced in the fluids in the production tubing I4 and the power tubing due to the reciproca-tory motion of the motor and pump pistons 26 and 28 as previously discussed.

Considering in more detail the manner in which pressure pulsations resulting from the reciprocatory motion of the motor and pump pistons 26 and 28 are absorbed, and referring particularly to Fig. 9 of the drawings, the numerals I55 and I56 indicate oscillograph curves showing respectively, typical pressure pulsations encountered in the power oil and production fluid columns when a pump such as the pump I9 is used without the shock absorber 22. It will be noted that the power oil pressure rises at the ends of the stroke of the motor and pump pistons 26 and 28 (see curve I55) and that the pump discharge pressure or production fluid pressure drops at the same time (see curve I56), the pressure pulsations in the two columns being of approximately the same magnitude and of opposite sign. The rise in pressure in the power tubing 28 and the drop in pressure in the production tubing I4 cause the shock absorber piston 43 to move upwardly against the pressure of the oil in the chamber 48 so that the energy producing such movement is absorbed by compression of the oil in this chamber, and also by compression to some extent of the production fluid. The net result is that the pressure in the power tubing 28 is decreased and the pressure in the production tubing I4 is increased, the resultant pressure in the two columns being approximately as indicated by the oscillograph curve I51 in Fig. 11. Thus, it will be apparent that, in effect, the shock absorber 22 causes the rise in power oil pressure and the drop in production fluid pressure to cancel out, which is an important feature of the invention.

It will be recalled that the radial passages III] in the tubular stem I8I on the shock absorber piston 43 are adaptedto move out of registry with the annular space I89 after a predetermined downward movement of the shock absorber piston. More specifically, the passages III) move out of registry with the annular space I08 when the piston 43 moves below its neutral or midposition. This cuts off communication between the lower end of the cylinder 89 containing the auxiliary piston 95 and the upper end of the motor cylinder 21 so as to interrupt operation of the pumping means 49. With this construction, the pumping means 49 will operate only until the desired pressure is built up in the chamber 48, which pressure balances the shock absorber piston 48 and moves it to its midposition. Consequently, if the shock absorber piston moves downwardly below its mid-position, due, for example, to an increase in production fluid pressure, the operation of the pumping means 49 is interrupted to prevent its pumping more liquid into the chamber 48 so that the shock absorber piston may return to its 'mid-position when the production fluid pressure returns to normal.

As previously mentioned, it is desirable to maintain the pressure in the chamber 48 at a high value, the reason for this being that the amount of energy which a liquid is capable of absorbing as it is compressed is directly proportional to the pressure of the liquid. The relationship between the variables involved may be expressed by the following equation:

W=PdP/K In this equation,

W=the energy absorbed per unit volume of the liquid,

P=the pressure of the liquid,

dP=the increase in pressure of the liquid, and

K=the bulk modulus of the liquid.

It will thus be apparent that the higher the pressure maintained in the chamber 48 by the pumping means 49, the greater will be the energy absorbed by compression of the liquid toa given extent, which is an important feature of my invention. v

Another feature of the invention resides in the provision of a shock absorber wherein the value of d? in the foregoing equation, as well as the value of P therein, is amplified, this being accomplished by making the cross-sectional area of the stem which extends into the chamber 48 small as compared to the area of the shock absorber piston 43 exposed to the power oil pressure. If an area ratio of 10, for example, is employed, it will be apparent that the increase in d? resulting from a given increase in the power oil pressure, 1. e., the pressure increase in the chamber 48 resulting from a given increase in the power oil pressure, will be ten times the increase in the power oil pressure to provide an amplification factor of ten for the shock absorber piston.

As will be apparent from the foregoing equation, since the energy absorbing capacity of the shock absorber varies with both P and dP, a very large capacity can be obtained with a small volume of liquid in the chamber 48 by making both P and dP large. Thus, if the shock absorber piston 43 and the pumping means 49 are provided with amplification factors of ten, the energy absorbing capacity of the device will be increased by a factor of one hundred, which is an important feature of the invention.

It will thus be apparent that by employing the pumping means 48 to convert a relatively low pressure into a relatively high value for P in the chamber 48 and by converting a relatively low pressure increase in the power oil pressure (or, conversely, a relatively low decrease in the production fluid pressure) into a relatively high value for d? in the chamber 48, a large energy absorbing capacity may be attained with a relatively small volume of liquid in the chamber 48, which is an important advantage of the invention. Thus, the volume of the chamber 48 may be much less than that of an air chamber, for example, having an equivalent energy absorbing capacity.

As previously indicated, the conduit or tube I I4 which provides fluid comunication between the motor cylinder 21 of the pump I9 and the pumping means 49 of the shock absorber 22 is provided with the coiled portion II5 to facilitate assembly of the shock absorber, the coiled portion II5 of the tube rendering the tube flexible and serving as a resilient means for performing a function to be described. Considering the manner in which the flexible tube II4 facilitates assembly of the shock absorber 22, one step in the assembly of the device involves threading the lowermost tube 53 of the shock absorber housing onto the fitting 58 which connects the shock 15 absorber to the pump is (prior to threading this fitting on the upper end of the pump). Subsequently, the flexible tube H4 is inserted through the fitting 58 into the tube 53 and the keys 15 on the insert 10 are inserted into the keyways l6 therefor, the lower end of the tube H4 previously having been permanently connected to the insert 10, as by soldering, for example. After the tube H4 has been inserted into the tube 53 of the shock absorber housing, the fitting H3 threaded into the bore I09 of the fitting 51 is assembled to secure the upper end of the tube H4 to the fitting 51, this being done prior to threading the fitting 51 into the upper end of the tube 53. The coiled portion H5 of the tube H4 is adapted to be extended during this operation. After the upper end of the tube H4 has been connected to the fitting 51 by means of the fitting H3, the insert I is pulled downwardly so that the keys l thereon disengage the keyways IS in the fitting 58, such downward movement being permitted by extension of the coiled portion H5 of the tube H4. With the insert 10 pulled downwardly in this manner, it may rotate relative to the fitting 58 to permit threading the fitting 51 for connecting the tubes 52 and 53 of the shock absorber housing into the upper end of the tube 53 of the housing. Subsequently, the insert Ill is rotated until the keys l5 thereon are aligned with the keyways in the fitting 58. Since the insert 10 was previously pulled down to stretch the coiled portion H5 of the tube H4, the coiled portion of the tube will then pull the insert 10 upwardly so that the keys 15 enter the keyways I6 and so that the shoulder i3 on the insert seats against the shoulder M on the fitting 58. The insert 10 will then rotate with the fitting 58 due to the action of the keys 15 in the keyways 16 so that the fitting 58 may be threaded onto the upper end of the pump it.

It will be understood that the fitting 51 for connecting the tubes 52 and 53 of the shock ab sorber housing may be threaded into the upper end of the tube 53 in the foregoing manner either before or after having been assembled with thecomponents of the shock absorber 22 thereabove.

Although I have disclosed an exemplary em bodiment of my invention herein for purposes of illustration, I do not intend to be limited specifically thereto since various changes, modifications and substitutions may be incorporated in the embodiment disclosed without necessarily departing from the spirit of the invention. For example, although I have disclosed the pressure in the chamber d8 as opposing the power oil pressure, it may be employed to oppose the production fluid pressure. Similarly, although I have shown the pumping means 59 as being adapted to pump oil from the power oil supply into the chamber (18, it may pump liquid from another source thereinto. Various other changes may also be made without departing from the spirit of the invention. Consequently, I hereby reserve the right to all changes, modifications and substitutions as properly come within the scope of the invention as set forth in the appended claims.

I claim as my invention:

1. In a fluid operated pumping unit, the combination of a pump adapted to be operated by a first fluid under pressure to pump a second fluid under pressure; a, shock absorber provided with movable fluid separating means therein; means for admitting the first fluid into said shock absorber on one side of said fluid separating means;

means for admitting the second fluid into said shock absorber on the opposite side of said fluid separating means; and means in said shock absorber for applying to at least a portion of one of said sides of said fluid separating means a fluid pressure exceeding the pressures of the first and second fluids.

2. A fluid'operated pumping unit, comprising: a pump adapted to be operated by a first fluid under pressure to pump a second fluid under pressure; a cylinder; a piston in said cylinder; means for exposing at least a portion of one end of said piston to the pressure of the first fluid; means for exposing at least a portion of the opposite end of said piston to the pressure of the second fluid; and means for applying to at least a portion of one of said ends of said piston a fluid pressure greatly exceeding the pressures of the first and second fluids.

3. In an apparatus for pumping fluid from a well, the combination of: a fluid operated pump in the well; a first tubing extending into the well and connected to said pump, said first tubing being adapted to convey operating fluid to said pump to operate same; a second tubing extending into the well and connected to said pump, said second tubing being adapted to convey from said pump production fluid discharged thereby; and a shock absorber, said shock absorber including movable fluid separating means provided with first and second surfaces on opposite sides thereof and provided with a third surface on one of said sides thereof, said shock absorber including means for exposing said first surface of said fluid separating means to fluid pressure obtaining in said first tubing, including means for exposing said second surface of said fluid separating means to fluid pressure obtaining in said second tubing, and including means for exposing said third surface ofsaid fluid separating means to a fluid pressure greatly exceeding the fluid pressures obtaining in said first and second tubings.

4. In a shock absorber for use in a well pumping apparatus which includes a fluid operated pump having first and second tubings connected thereto, the first tubing being adapted to convey operating fluid to the pump to operate same and the second tubing being adapted to convey from the pump production fluid discharged thereby, the combination of: movable fluid separating means having first and second surfaces on opposite sides thereof and having a third surface on one of said sides thereof; means for exposing said first surface of said fluid separating means to fluid pressure obtaining in the first tubing; means for exposing said second surface of said fluid separating means to fluid pressure obtaining in the second tubing; and means for exposing said third surface of said fluid separating means to a fluid pressure greatly exceeding the fluid pres sures obtaining in the first and second tubings.

5. In a device for absorbing pressure variations in first and second fluids, the combination of: movable fluid separating means having first and second surfaces on opposite sides thereof and having a third surface on the same side thereof as said second surface, the area of said third surface being small as compared to the areas of said first and second surfaces; means for applying the pressure of the first fluid to said first surface of said fluid separating means; means for applying the pressure of the second fluid to said second surface of said fluid separating means; and means for applying to said third surface of said fluid separating means a fluid pressure ex ceeding the pressures of the first and second fluids.

6. A device as set forth in claim wherein the product of the pressure of the first fluid and the area of said first surface substantially equals the product of the pressure of the second fluid and the area of said second surface plus the product of the pressure applied to said third surface and the area of said third surface.

7. In a device. for absorbing pressure variations in first and second fluids, the combination of: a housing; movable fluid separating means in said housing, said fluid separating means having first and second surfaces on opposite sides thereof and having a third surface on one of said sides thereof; means for applying the pressure of the first fluid to said first surface of said fluid separating means; means\for applying the pressure of the second fluid to said second surface of said fluid separating means; a source of fluid pressure; means for applying to said third surface of said fluid separating means the fluid pressure obtaining at said source; and means in said housing for maintaining fluid pressure at said source.

8. A device as set forth in claim 7 wherein the means last mentioned comprises pumping means for delivering fluid under pressure to said source.

9. A device as set forth in claim 8 wherein said pumping means is operable by the first and second fluids.

10. A device as set forth in claim 7 wherein the means last mentioned is carried by said movable fluid separating means.

11. In a device of the character described, the combination of: a cylinder; a piston reciprocable in said cylinder; a source of fluid pressure; means for applying to at least a portion of the area of one end of saidpiston the fluid pressure obtaining at said source; and pumping means including a plunger carried by and movable relative to said piston for maintaining fluid pressure at said source.

12. A device as set forth in claim ll wherein said pumping means is fluid operated, said device including means for connecting one side of said plunger to a source of alternating pressure.

13. In a shock absorber, the combination of: a cylinder; a piston reciprocable in said cylinder; a chamber for a fluid under'pressure connected to said cylinder; pumping means including a plunger carried by and movable relative to said piston for maintaining fluid pressure in said chamber; and means for applying the fluid pressure in said chamber to at least a portion of one end of said piston.

14. A shock absorber as set forth in claim 13 wherein said piston is provided with a tubular stem which extends into said chamber, said stem communicating at one end with the interior of said chamber and at its other end with an outlet of said pumping means.

15. A shock absorber as set forth in claim it wherein said pumping means is fluid operated. passage means being provided for connecting one end of said plunger to a source of alternating fluid pressure.

16. In a shock absorber, the combination of: a. main cylinder; a main piston reciprocable in said main cylinder and provided with an auxiliary cylinder therein; a chamber for a fluid under pressure connected to said main cylinder; fluid operated pumping means carried by said .nain piston and communicating with the in- 18 terior of said chamber for maintaining fluid pressure in said chamber, said pumping means including an auxiliary piston reciprocable in said auxiliary cylinder; means for applying an alternately increasing and decreasing fluid pressure to one end of said auxiliary piston; and means for applying the fluid pressure in said chamber to at least a portion of one end of said main piston.

1'7. A shock absorber as set forth in claim 16 wherein said main piston is provided with a tubular stem which extends into said chamber, said stem communicating at one end with the interior of said chamber and at its other end with said auxiliary cylinder.

18. In a fluid operated pumping unit, the combination of: a fluid operated pump provided with a motor cylinder having a motor piston reciprocable therein and provided with means for pcriodically admitting an operating fluid under pressure into one end of said motor cylinder; a shock absorber cylinder; a shock absorber piston reciprocable in said shock absorber cylinder; a chamber for a fluid under pressure; fluid operated pumping means for maintaining fluid pressure in said chamber; passage means communicating at one end with said one end of said motor cylinder for conveying operating fluid to said pumping means to operate same; and means for applying the fluid pressure in said chamber to at least a portion of one end of said shock absorber piston.

19. A fluid operated pumping unit as defined in claim 18 wherein said shock absorber piston is provided with an auxiliary cylinder therein, wherein said pumping means includes an auxiliary piston reciprocable in said auxiliary cylinder. and wherein said passage means communicates at its other end with one end of said auxiliary cylinder.

20. In a shock absorber, the combination of: a cylinder; a piston reciprocable in said cylinder; a chamber for a fluid under pressure; an axially extending, tubular stem on said piston, the crosssectional area of said stem being exposed to the fluid pressure in said chamber and being small as compared to the cross-sectional area of one end of said piston; and means for delivering fluid under pressure to said chamber through said tubular stem.

21. In a fluid operated well pumping device, the combination of z a first fluid operated pump adapted to be disposed in a, well so as to pump well fluid therefrom, and having a first cylinder and a first piston in said cylinder; a second fluid operated pump adapted to be disposed in the well, said second pump having a second cylinder and a second piston therein; and passage means for connecting one end of said second cylinder in continuous fluid communication with one end of said first cylinder.

22. In a device adapted to be used with a fluid operated pump in a well, the pump being operated from a source of operating fluid under high pressure, the combination of: a chamber filled with liquid under fluid pressure higher than that of said source; a movable wall, one side of which is adapted to communicate with said source and be exposed to the fluid pressure thereof; plunger means connected to the other side-of'said wall and extending into said chamber and movable with respect thereto, said plunger means having an effective cross-sectional area exposed to the fluid pressure in said chamber which is substantially smaller than the effective cross-sectional area of said one side of said wall exposed to the fluid pressure of said source; and pumping means including a plunger carried by and movable relative to said movable wall for delivering liquid to said chamber to maintain said higher fluid pressure therein 23. In a fluid operated pumping device, the combination of: a fluid operated pump having a fluid port therein in one end thereof; a tubular member adapted to be threadedly connected to said end of said pump; a fitting adapted to be threadedly connected to the other end of said member, said fitting having a fluid passage therein; and a flexible fluid conduit in said member for connecting said port and said passage, said flexible fluid conduit including a coiled portion.

24. In a fluid operated pumping device, the combination of a fluid operated pump having a fluid port therein in one end thereof; a tubular member adapted to be threadedly connected to said end of said pump; a fitting adapted to be threadedly connected to the other end of said member, said fitting having a fluid passage therein; a flexible fluid conduit in said member for connecting said port and said passage, said flexible fluid conduit including a coiled portion; and means for releasably comiecting said conduit to said pump.

25. In a shock absorber adapted to be connected to a fluid operated pump, the combination of: a tubular member adapted to be threadedly connected at one end to one end of the pump; a fitting adapted to be threadedly connected to the other end of said member; an insert adapted to move in said member from said one end thereof toward said other end thereof from a first position to a second position; means for limiting movement of said insert beyond said second position; and resilient conduit means in said member adapted to be rigidly connected at one end to said insert and at its other end to said fitting for biasing said insert toward said second position.

26. A shock absorber as set forth in claim 25 wherein said insert is rotatable relative to said member when it is in its said first position so as to permit rotation of said fitting relative to said member, whereby to permit threadedly con-- necting said fitting to said other end of said member.

27. A shock absorber as set forth in claim 26 including means for preventing rotation of said insert relative to said member when it is in its said second position.

28. In a shock absorber for absorbing pressure variations in a first fluid normally of one pressure and a second fluid normally of another, lower pressure, the combination of: a cylinder; a piston in said cylinder having on one side thereof a first surface and having on the other side thereof second and third surfaces, the area of said third surface being less than the areas of said first and second surfaces; means in-- cluding a passage communicating with said cylinder on said one side of said piston for exposing said first surface to the first fluid; means including a passage communicating with said cylinder on said other side of said piston for exposing said second surface to the second fluid; and means for exposing said third surface to a third fluid of a pressure suflicient to balance the normal pressure force differential applied to said piston by the first and second fluids, including a chamber confining said third fluid so that said third fluid acts resiliently on said third surface to absorb any differences between said normal pressure force differential and abnormal pressure force differentials resulting from variations in the pressures of the first and second fluids from normal.

29. In an apparatus for pumping fluid from a well, the combination of: a fluid operated pump in the well; a' first tubing extendin into the well and connected to said pump, said first tubing being adapted to convey operating fluid to said pump to operate same; a second tubing extending into the well and connected to said pump, said second tubing being adapted to convey from said pump production fluid discharged thereby; and a shock absorber, said shock absorber including movable fluid separating means provided with a first surface on one side thereof and second and third surfaces on the opposite side thereof, the area of said third surface being less than the areas of said first and second surfaces, said shock absorber including means for exposing said first surface of said fluid separating means to fluid pressure obtainin in said first tubing, including means for exposing said second surface of said fluid separatin means to fluid pressure obtaining in said second tubing, and including means for exposing said third surface. of said fluid separating means to a third fluid, said shock absorber further including a chamber which confines the third fluid so that said fluid separating means varies the pressure in said chamber in response to variations in the fluid pressures obtaining in said first and second tubings to balance the fluid pressures applied to said fluid separating means.

30. In ashock absorber for a fluid-operated pump adapted to be operated by fluid at one generally constant pressure level and to discharge fluid at another generally constant pressure level, the combination of: movable means for separating the fluid at said one generally constant pressure level from the fluid at said other generally constant pressure level; and means for applying to said movable means in a direction opposing the higher of said pressure levels the pressure of a third fluid, includin a chamber for confining said third fluid.

CLARENCE J. COBERLY.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,623,239 Galbreath Apr. 5, 1927 1,991,595 Creveling Feb. 19, 1935 2,022,859 Herbsman et al. Dec. 3, 1935 2,036,464 Dodge Apr. 7, 1936 2,134,174 Coberly Oct. 25, 1938 2,134,735 Reinhold Nov. 1, 1938 2,196,993 Kidder Apr. 16, 1940 2,311,157 Coberly Feb. 16, 1943 FOREIGN PATENTS Number Country Date 403,846 Great Britain Jan. 4, 1934 

